hwpmc_amd: split allocation paths

[mhorne]

Summary

The legacy and modern (pmu-events) allocation paths are distinct.
Further clarify this by splitting the function in two.

[afscoelho_gmail.com]

sys/dev/hwpmc/hwpmc_amd.c

413

should we not check for PMC_F_EV_PMU here also?

if ((a->pm_flags & PMC_F_EV_PMU) != 0)
              return (EXTERROR(EINVAL,
                  "AMD pmu-events are not supported on this CPU"));

419

PMCDBG2(MDP, ALL, 1,"amd-allocate-legacy ri=%d caps=0x%x", ri, caps);

468

PMCDBG2(MDP, ALL, 2, "amd-allocate-legacy ri=%d -> config=0x%x", ri, config);

505

I think you need to put this check also in the beginning of the legacy path, otherwise if a client fills all core counters, a wrong allocation can happen on the L3 row. For example, the command

pmcstat -s k8-fr-retired-x86-instructions -s k8-bu-cpu-clk-unhalted \
        -s k8-dc-access -s k8-dc-miss -s k8-ic-miss \
        -s k8-fr-retired-taken-branches -s k8-ic-fetch  sleep 5

will put k8-ic-fetch on an L3 counter. Today it returns an error (expected):

❯ sudo pmcstat -s k8-fr-retired-x86-instructions -s k8-bu-cpu-clk-unhalted \                                                                                                                                                                        -s k8-dc-access -s k8-dc-miss -s k8-ic-miss \                                                                                                                                                                                               -s k8-fr-retired-taken-branches -s k8-ic-fetch  sleep 5                                                                                                                                                                             pmcstat: ERROR: Cannot allocate system-mode pmc with specification "k8-ic-fetch": Invalid argument (No PMC row accepted the allocation request)